The present invention relates to titanium alloys and products made from titanium alloys, and more particularly to a castable, weldable, high-modulus titanium alloy and associated products. One embodiment of the present invention is particularly useful for manufacturing golf club heads.
Titanium alloys are used in a wide range of products from aerospace components to bicycle parts. Titanium parts can be fabricated using several different techniques, such as casting, forging, milling, or powder metallurgy. The optimal alloy composition depends on the intended product and fabrication technique. For example, ductility may be an important characteristic for a mill product made by a rolling process, while melt fluidity may be more important when producing cast products. Multiple types of fabrication processes, such as welding to a cast titanium alloy part, place additional constraints on the alloy composition. In such an instance, the alloy must have good welding properties, as well as good casting properties. Additionally, it may be desirable to improve a material parameter of the alloy, such as modulus, hardness, strength, or toughness, based on the intended use of the part made from that alloy.
In some instances, an alloy exhibiting good material parameters for an intended purpose may be incompatible with a fabrication process. For example, it is desirable that a golf club head have a high modulus, so that the energy of the swung golf club is efficiently transferred to the golf ball when it is hit. A titanium alloy containing 8 weight percent aluminum, 1 weight percent vanadium, and 1 weight percent molybdenum (Ti 8-1-1) has a modulus of about 17.times.10.sup.6 psi, which is appropriate for use in a golf club head. However, golf club heads are often cast, and Ti 8-1-1 does not exhibit good casting properties. A titanium alloy containing 6 weight percent aluminum and 4 weight percent vanadium (Ti 6-4) has better casting properties, but a lower modulus (16.5.times.10.sup.6 psi), making it a less attractive material for use in a golf club head. Additionally, vanadium is an expensive alloying element, accounting for approximately 10% of the material cost of the Ti 6-4 alloy at current market prices, making this alloy even less attractive for high-volume use in a recreational product, such as a golf club head.
Therefore, a titanium alloy with the modulus of Ti 8-1-1 and the castability of Ti 6-4 would be desirable. It would be further desirable that this alloy contain less expensive alloying components than present alloys. It is also desirable that such an alloy exhibit good weldability.